I only think that bitcoin can be replaces of this two great coins in market once it was dead. They are capable to stand by its own feet because they are already used it and recognize in the cryptosphere with there respective featured design process or kind of coin are they.
The thing is bitcoin will not dead very soon, i think if bitcoin dead then it means cryptocurrency will be in danger too, because bitcoin is like the father of cryptocurrency and if something bad happen to bitcoin, it always affect other cryptos.
In my opinion, no altcoins can replace bitcoin even ethereum and ripple too.